1. Field of the Invention
The present invention relates in general to control systems of automatic transmissions, and more particularly to control systems of stepwise variable automatic transmissions.
2. Description of the Related Art
In order to clarify the features of the present invention, the control system disclosed in Japanese Laid-open Patent Application (Tokkaihei) 9-170654 will be briefly described in the following.
In the Laid-open Patent Application, there is disclosed a control system that controls operation of a stepwise variable automatic transmission with the aid of learning control. In the control system, a piston stroke time needed for completion of engagement of a given frictional element, such as clutch, brake or the like, is detected or derived, and if the detected piston stroke time shows a value suitable for controlling or suppressing a shift shock, OK judgment is issued, while if the detected piston stroke time shows a value other than the suitable time, the instruction value for a hydraulic pressure to the frictional element is corrected by means of a learning control to cause the piston stroke time to show the suitable value. For ease of description, correction by means of learning control will be referred to “learning correction” in the following.
For designing an automatic transmission that carries out a learning correction like the learning correction as disclosed in the above-mentioned Japanese laid-open Patent Application, a map (viz., learning correction map) is provided which shows a relation between engine torque data received from an engine controller and predetermined piston stroke times. With practical usage of the learning correction map, the learning correction is carried out in accordance with an operation condition of an associated motor vehicle.